(1) Field of the Invention
This invention relates generally to a countermeasure device, and more particularly to a countermeasure device including an air bag hover system and one or more low frequency acoustic projectors, both of which are supplied with air from a high pressure air source in order to actively compensate for external water pressure at any depth.
(2) Description of the Prior Art
The use of acoustic countermeasure devices in undersea warfare to protect submarines is common throughout the world. Such countermeasure devices are required to rise or lower at a predetermined rate, hover in place at a predetermined depth, and produce either a high or low frequency sound. Generally, high frequency sounds are emitted by countermeasure devices in order to disrupt a projectile such as a torpedo, while low frequency sounds are emitted to disrupt sonar. At low frequencies, such systems must move large amounts of water in order to produce the proper acoustics to shield the submarine, or to give the sonar multiple targets. A problem arises when utilizing such low frequency devices at depths of about 500 feet or more. Specifically, the acoustic projectors rapidly vibrate in order to produce the low frequency sound and, at deep sea, the external water pressure can interfere with such vibration, causing the sound emitted to be distorted or, in extreme cases, to fail completely. Therefore, countermeasure devices which operate at low frequencies are traditionally provided with a pressure compensating system in order to avoid depth limitations. For example, U.S. Pat. No. 4,524,693 to McMahon et al. discloses an underwater transducer including a water bladder assembly within the transducer which forms a passive internal pressure compensation system to protect the transducer against collapse under excessive ambient pressures. U.S. Pat. No. 5,103,432 to Percy discloses a low frequency, high powered underwater sound source including a housing having a loud speaker disposed therein. A bladder is disposed over the loud speaker which contains a pressurized, non-liquid sound transmission medium. Also disclosed is a fill system for filling the bladder with the sound transmission medium, a vent system for venting the bladder of the sound transmission medium, and a differential pressure sensor for comparing the pressure in the bladder with the ambient underwater pressure. U.S. Pat. No. 5,140,560 to Percy discloses an acoustic source apparatus including an acoustic transducer which is enclosed in a substantially rigid and watertight enclosure to resist the pressure of the water on the transducer and to seal the transducer from the water. The enclosure has an opening through which acoustic signals pass and over which is placed a resilient, expandable and substantially water-impermeable diaphragm. Pressurized gas, regulated at slightly above ambient pressure, is supplied to the enclosure and the diaphragm to compensate for underwater ambient pressures. Controls are used to selectively fill, as well as vent the enclosure and diaphragm during system descent and ascent, respectively.
While generally acceptable, such systems often utilize expensive electronics, air cylinders and valves for active pressure compensation, in addition to the hovering system which operates to move and hover the device in place. Such systems have increased weight (which can effect maneuvering), tend to be costly and, due to their complexity, may have reduced reliability.
There is therefore needed an improved countermeasure device for low frequency operation without depth limitation and which is lighter, less costly, and more reliable than existing countermeasure devices.